Gravity and forced hot air furnace



May 20, 1969 c. w. FRAIM GRAVITY AND FORCED HOT AIR FURNACE Sheet 013 Filed Nov. 20, 1967 PIC-3.2

I NVENTOR C4 m ra/v l1. fen/M BY ATTORNEYS y 0, 1969 c. w. FRAIM 3,444,854

GRAVITY AND FORCED HOT AIR FURNACE Filed Nov. 20, 1967 Sheet .2 01 s J2 F I e. 3

mlvr 26 I NVENTOR CZ/A/TO/V 14 fPA/M ATTORNEYS May 20, 1969 Filed Nov. 20, 1967 C. W. FRAIM GRAVITY AND FORCED HOT AIR FURNACE Sheet ,2 01'3 F'IG.6

l NVENTOR Cz/n ro/v n4 fen/M ATTORNEYS United States Patent 3,444,854 GRAVITY AND FORCED HOT AIR FURNACE Clinton W. Fraim, Sturgis, Mich., assignor to Motor Wheel Corporation, Lansing, Mich, a corporation of Ohio Filed Nov. 20, 1967, Ser. No. 684,359 Int. Cl. F24h 3/06, 3/00 US. Cl. 126-110 Claims ABSTRACT OF THE DISCLOSURE A hot air furnace of the sealed combustion space heater type fueled by gas or oil which can be operated as a gravity or forced circulation system, or both. The furnace is adapted for upright recessed mounting in a side Wall of the principal room to be heated and has a sealed duct combustion system which includes a combustion chamber surrounded at its sides and rear by a primary air heating chamber. The primary chamber communicates with the room through upper and lower openings in the front panel of the furnace to permit gravity induced air circulation from the room into the heater, upwardly past the combustion chamber and thence outwardly back into the room again to thereby heat the room by gravity convection heating as well as by radiant heating. The furnace also has a blower connected to the lower outlet end of a secondary air heating chamber which surrounds the primary air chamber. The inlet of the secondary chamber is positioned directly above the room outlet of the primary air chamber. When the blower is in operation, a portion of the hot air convection currents issuing from the outlet of the primary chamber into the room is immediately sucked from the room back into the furnace Via the inlet of the secondary air chamber and is then drawn downwardly therethrough to the blower, in counter flow heat exchange relation with the heated air flow in the primary chamber, and is then forced into a sub-floor distribution duct system to heat other spaces in the trailer or home. The sealed duct combustion system includes a combustion air intake chamber separating the secondary chamber from the exterior of the furnace to provide both insulation and economizer operation.

An object of the present invention is to provide a space heater designed primarily for heating relatively small enclosures such as house trailers which is simple and compact in construction and which reliably and economically provides two in one operation, i.e., combining the principles of radiant heating-convection hot air heating with forced hot air heating so as to alford the luxury of forced air wherever electrical power is readily available to operate the furnace blower but retaining the capability of eflicient radiant-convection heating when camping in remote areas or on other occasions when no electrical power is available.

Another object is to provide a furnace of the above character which is attractive in appearance, adapted for recessed side wall mounting and which meets sealed combustion system code requirements.

Still another object is to provide a furnace of the above character in which a blower is operable to provide forced air operation as desired and yet, regardless of the operation or in operation of the blower, the circulation of heated air passing in contact with the combustion chamber heat exchanger is unidirectional and uninterrupted, thereby eliminating the undesirable heat exchanger surface stresses, the expensive safety switch circuitry normally required to accommodate blower malfunctions and the bafiies or moving dampers which are subject to malfunctioning through friction, wear and/or lint.

"ice

Other objects as Well as features and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a fragmentary perspective view illustrating a furnace constructed in accordance with the present invention mounted recessed in a hollow or closet wall of a travel trailer with its front panel flush with the surface of the interior wall.

FIG. 2 is a front elevational view of the furnace with portions of its front panel broken away to illustrate interior detail.

FIG. 3 is a fragmentary vertical sectional View taken on the line 33 of FIG. 2 illustrating the interior components in side elevation with portions broken away to illustrate details.

FIG. 4 is a horizontal section taken on the line 4-4 of FIG. 3.

FIG. 5 is atop plan view of the furnace.

FIG. 6 is a fragmentary perspective view illustrating in solid lines the interior casing components and exterior top and bottom walls of the furnace, and in phantom the exterior front, side and rear panels of the outer casing of the furnace.

Referring in more detail to the accompanying drawings, FIG. 1 shows an exemplary but presently preferred form of a wall furnace 10 constructed in accordance with the present invention mounted with zero clearance in a recess provided in the interior wall 12 of a travel trailer or the like so that the front panel 14 of the furnace is flush with wall 12. Furnace 10 is adapted to rest on the finish flooring 16 of the trailer with its back wall against the exterior vertical wall 18 of the trailer and with its top wall disposed adjacent or spaced somewhat below the ceiling wall 20 of the trailer.

As best seen in FIGS. 3-6 inclusive, the framework of the furnace consists primarily of sheet metal partitions and easing components interconnected in a spot welded self-supporting assembly. The cabinet or outer casing of the furnace comprises a generally rectangular upright sixsided box made up of front panel 14, vertical side walls 22 and 24, rear wall 26 and top and bottom walls 44 and 32. Side walls 22 and 24 and rear wall 26 are formed from a single metal sheet as best seen in FIGS. 4 and 5, and vertically extending outwardly directed flanges 28 and 30 respectively. Bottom wall 32 of the outer casing in a rectangular piece of sheet metal formed with a dependent peripheral flange 34 adapted to nest within side and rear Wall 22, 24 and 26 of the outer casing and provides a compartment for receiving a compression gasket (not shown) which forms a seal against floor jacket adapter 38 (FIG. 3). A downwardly flanged rectangular opening 36 is formed in wall 32 to receive discharge outlet 146 of blower housing (FIG. 3) therethrough which in turn connects with the plenum duct 40 of a conventional sub-floor distribution duct 42 (FIGS. 1 and 3).

Top wall 44 of the outer casing is upwardly flanged along its side and rear edges and nests within the side and rear walls 22, 24 and 26 of the outer casing. Wall 44 comprises a horizontal panel 46 with a circular aperture therein which receives a vertically extending combustion air duct collar 48 therethrough. Collar 48 has a radial flange 50 at its lower end which seats against the undersurface of panel 46 and has an outward flare 52 at its upper end for receiving a suitable wind deflecting combination inlet and outlet vent cap 54 (FIG. 1), preferably that disclosed in the co-pending patent application of Paul W. Fair and myself, Serial No. 538,066, filed March 28, 1966, now Patent No. 3,361,051, granted January 2, 1968 and assigned to the assignee herein. The front edge of panel 46 is spaced rearwardly from front panel 14 and is joined to a vertical panel 56 which extends downwardly therefrom. Panel 56 is joined at its lower edge to a horizontal panel 58 which extends outwardly therefrom so that the forward edge of panel 58 projects between a pair of the upwardly and inwardly inclined horizontal louvers 60 formed in the upper section 62 of panel 14. Top wall 44 thus has a stepped-down configuration which co-operates with the three uppermost louvers 60 to form a vent opening interconnecting the interior room space with the dead air space located between walls 12 and 18 and above furnace 10.

Furnace 10 has an inner casing disposed within the outer casing and made up in part of a horizontal top wall 70 (FIGS. 3 and 6), parallel vertical side walls 72 and 74 and a rear wall 7 6, walls 72, 74 and 76 preferably being formed from one sheet of metal. Flanges 78 and 80' are formed along the outer vertical edges of walls 72 and 74 so as to extend outwardly and overlap flanges 28 and 30 respectively (FIGS. 4 and The lower edges of side walls 72 and 74 have horizontal, outwardly directed flanges 82 and 84 respectively (FIGS. 4 and 6) the outer edges of which contact side walls 22 and 24 respectively. The inner casing also includes a vertical panel 86 extending vertically downwardly from a lip 88, which overlaps the lower edge of panel 86, to a horizontal flange 90 thereof which rests on bottom wall 32. Panel 86 extends horizontally from wall 22 to a wall 24 and has side flanges 92 and 94 respectively secured to these walls. The lower edge of panel 86 has a vertical lip 96 (FIG. 6) which extends into opening 36 and which is secured to the rear flange of wall 32 to locate panel 86 in proper alignment with wall 7 6.

The front edge 71 (FIG. 6) of top wall 70 projects outwardly between a pair of the louvers 60 of upper front panel section 62. Section 62 is clamped along its side edges by vertically extending channel members 100 (FIG. 5). The lower section 102 of front panel 14 is readily removable, and, as best seen in FIG. 3, overlaps at its upper and lower edges inside the lower edge of panel 62, has two vertical rows of horizontally extending and upwardly and inwardly inclined louvers 106.

The interior space between the outer and inner casing top walls 44 and 70 and between rear walls 26 and 76 is divided by an inverted L-shaped partition made up of a horizontal panel 110 joined at its rear edge to a vertical panel 112 (FIGS. 3 and 6). Panels 110 and 112 have side flanges spot welded to the respectively adjacent side walls 22 and 24 of the outer casings. The front edge 113 (FIG. 3) of panel 110 underlaps and is secured to the rear edge of panel 58. The lower edge of panel 112 is integrally joined to a flange 114 which extends horizontally to wall 26 and is secured thereto along a dependent flange 116. An oval duct 120 extends horizontally in sealed relation through an oval aperture 122 (FIG. 6) in panel 86 and telescopes at its rear end onto a similarly shaped axial flange of an adapter collar 124 (FIG. 3) WhlCh is inserted trough an oval aperture near the lower end of panel 112. The front end of duct 120 connects in sealed relation to an inlet in the rear side of a burner box 126 (FIGS. 2 and 3). Burner box 126 is suspended from a box-like combustion chamber 128 which in turn is supported by brackets 129 secured to walls 72 and 74 with the four vertical sides of combustion chamber 128 spaced from the respectively adjacent vertical walls of the inner casing of the furnace. Burner box 126 and combustion chamber 128 are conventional and therefor not described in detail herein, and may be designed to burn liquified propane gas and be equipped with the usual gas burner and associated controls. Combustion chamber 128 1s of conventional finned sheet metal heat exchanger construction and communicates at its upper end with a cylindrical flue pipe 130 which extends vertically upwardly centrally of the furnace in sealed relation through registering openings in walls '70 and 11! and coaxially into collar 48 for telescopic connection to a flue duct of roof cap 54.

A flow deflecting bafiie 132 (FIGS. 2, 3, 4 and 6) is mounted within the upper region of the inner casing above combustion chamber 128 and is suitably apertured to receive flue 130 therethrough. Baflle 132 has its forward edge 134 inserted between a pair of the louvers 60 of panel 62 and is secured by side flanges to side walls 72 and 74. A flange 136 extends vertically from the rear edge of 'baflle 132 and is spaced about inch from rear wall 76.

A conventional blower 138, having a centrifugal impellor 139 journalled in a housing 140 and an electric drive motor 142, is mounted at the lower end of the inner casing with the blower inlet registered with a corresponding aperture 144 in panel 86 (FIG. 6), and with the blower outlet 146 projecting downwardly into floor opening 36. A conventional transformer and power supply unit 148 is also mounted in this lower forward compartment formed between side walls 22, 24, bottom wall 32 and the removable front panel section 102.

When non-blower heating operation is desired, or when electrical power is not available, furnace 10 is efficiently operable as a radiant-convection hot air space heater with blower 138 turned 013?. When so operated, fuel is supplied under pressure to the gas burner in burner box 126 from the supply of bottle gas and combustion takes place in chamber 128. As indicated by the arrows in FIG. 3, fresh air for supporting combustion is taken from above the roof of the trailer via a combustion air duct comprising the annular space between collar 48 and flue pipe 130, the overhead space between top walls 44 and 110, the rear wall space between vertical panels 26, 112, 22 and 24, thence through duct 120 into burner box 126. The products of combustion are conducted in sealed relation from chamber 128 via flue pipe 130 to the outlet flue of roof cap 54 and escape therefrom to outside atmosphere above the roof of the trailer. This flow of fresh air from above the roof downwardly through the sealed combustion system and back again to the roof occurs as a natural draft flow created by the gravity induced pressure difi'erential between the cold heavy incoming air and the less dense heated products of combustion. It will be seen that the entire combustion system is sealed from the other interior spaces of the furnace as well as from the interior of the trailer so as to meet sealed combustion code requirements.

The furnace compartment in which combustion chamber 128 is located forms a primary air heating chamber which is defined by inner casing walls 72, 74, 76, 70 and 62, the bottom end of this chamber being open to the front compartment defined by panel 86, panel 102 and the portions of the exterior casing side walls 22 and 24 disposed below flanges 82 and 84. The heat generated within combustion chamber 128 is conducted to the exterior surface of the thin sheet metal walls of the chamber where it radiates in all directions in the primary chamber to heat the surrounding air and sheet metal panels 72, 74, 76, 132 and 62 by radiation, some of the radiant heat passing through louvers 60 and panel 62 to radiantly heat the room space in which furnace 10 is located. The air in the primary chamber is heated by radiation and conduction from chamber 128 and, as indicated by the arrows in FIG. 3, flows upwardly on all sides of the combustion chamber and impinges against baflle 132 which serves as a heat distribution baflle to promote even distribution of the heated air issuing from the primary chamber outlet, i.e., the temperature of the heated air issuing from between each adjacent pair of louvers 60 from wall 70 down to the imperforate portion 62 of the front panel is maintained substantially uniform. Baflle 132 directs some of the heated air outwardly through louvers 60 disposed below the front edge 134 of the baflfle, and directs the remainder of the convection flow rearwardly against wall 76 where it flows around the rear edge 136 of the baffle into the uppermost region of the primary heating chamber, and thence flows forwardly beneath wall 70 out through louvers 60 into the room space. The heated air rising past rear edge 136 tends to be uniformly distributed between baflle 132 and wall 70 by the turbulence caused by the baflie. This convection flow causes the heavier, cold room air to be drawn into the primary chamber via the inlet formed by the louvers 106 of the removable front panel 102, the cool air flowing upwardly into the open bottom of the primary chamber and serving to cool motor 142, transformer 148 and other components disposed in the front equipment compartment.

When it is desired to operate furnace as a part of a forced hot air heating system to distribute heated air to other room spaces of the trailer or dwelling remote from the furnace, motor 142 is connected to a suitable source of electrical power by a thermostatic control and/ or a manually operated switch to thereby turn on blower 138. The blower draws air from the lower end of a secondary air heating chamber which is defined at the top and rear by panels 58, 110, 112, 114 and wall 26 below panel 114, and at the bottom and front by panels 70, 76, 86 and wall 32 between panels 86 and 26. The sides of the secondary chamber are formed by walls 22 and 24, and by panels 72 and 74, the secondary chamber extending forwardly to the front panel 14 above flanges 82 and 84 so as to surround the primary chamber on three sides as well as from above. The inlet to the secondary chamber is through louvers 60 disposed between panels 58 and 70, which is directly above the primary chamber outlet.

The counter-gravitational forced air flow induced through the secondary air chamber by blower 138 (as indicated by the arrows in FIG. 3) causes heated air to be drawn into the secondary chamber inlet from the room space. Most of this heated air is made up of air issuing from primary chamber outlet which is immediately sucked back into the furnace. This pre-heated air then flows downwardly in heat exchange relation with the convection air rising in the primary chamber as it is drawn to the blower inlet 144, thereby raising the temperature in the secondary air heating chamber. This in turn increases the heat exchange through panels 110 and 112 to the incoming fresh air travelling down the combustion air duct, but this is not sufficient to materially increase the temperature of the combustion air in response to blower operation. Due to the fact that furnace 10 operates as a radiant heater, and also because some of the heated convection air issuing from the primary chamber outlet escapes the suction flow into the secondary chamber inlet, the living space in the trailer in Which furnace 10 is located continues to be heated even while blower 138 is forcing the heated secondary air down through the blower outlet 146 into sub-floor duct 42 for distribution beneath the floor of the trailer to the remote spaces such as the bathroom and bedrooms of the trailer.

From the foregoing description, it will now be understood that one important feature of the present invention is the fact that air flow through the primary air chamber is continuous, always in the same direction and is primarily caused by gravity convection flow occurring in response to combustion occurring in chamber 128. This is true Whether or not blower 138 is operating. When both blower 138 and the burner 126 are turned on, there is very little if any increase in the rate of flow through the primary chamber since the secondary chamber inlet draws from the entire room. Hence, the convection flow through the primary chamber is not materailly altered by operation of the blower and is still gravity induced and upwardly along the four vertical sides of the combustion chamber. Thus turning the blower on or off does not interrupt the natural convection air flow passing in contact with heat exchanger 128 nor does this cause a reversal of the direction of air flow in the convection zone. As a result heat exchanger surface stresses are greatly reduced, thereby prolonging the life of the heat exchanger and reducing the chances of a rupture occurring in sealed joints of the system.

Moreover, since the blower is not a functional part of the convection heating process, there is no need for costly safety switch circuitry which otherwise would be required to shut down the furnace in the event of blower failure in order to safeguard against furnace overheating. This feature also eliminates the need for flow directing bafiles or moving dampers hitherto required for switching air flow from one zone to another, items which are not only expensive but subject to malfunctioning through friction, wear or and/or lint accumulation.

Due to the secondary chamber inlet being located near the top of the furnace, above the hot air outlet from the primary chamber, hot air is drawn from the layer of room air next to the ceiling, thereby alleviating uncomfortable stratification effects when the furnace is being operated as a forced hot air system, or in the summertime when the blower is operated with the burner shut-off. Since some cooler air from the room is drawn into the secondary chamber along with the heated air issuing from the primary chamber outlet, the counter-flow forced circulation in the secondary air heating chamber causes a reheating of the previously heated air as it passes downwardly on its way to the blower inlet so that adequate blower outlet temperatures are maintained. The wraparound disposition of thesecondary chamber relative to the primary chamber also provides an insulating effect between the primary chamber and the exterior walls of the furnace. Nevertheless, even though forced air flow in the secondary chamber increases the cooling effect on the primary chamber and the pre-heat of the combustion air travelling downwardly in the combustion air duct to the combustion chamber, there is no change in the combustion chamber or primary chamber conditions in response to blower operation, and total B.t.u. output of the furnace is not materially increased by blower operation. When the burner is on and the blower is not operating there is a slight reverse air flow through the secondary chamber due to leakage from the blower outlet upwardly into the secondary chamber which contributes primarily to the insulating function of the secondary air chamber rather than to the heat output of the furnace. This low volume flow of cool air is drawn from the rooms of the trailer remote from the furnace via duct 42 and is drawn upwardly through the secondary chamber by the aspirating effect of hot air issuing from the primary chamber outlet as well by convection flow due to being heated as it rises in the secondary chamber. This provides a low volume, low velocity stream of air issuing from the secondary chamber inlet which is cooler than the su-bjacent stream of hot air issuing from the primary chamber outlet. These streams immediately intermix, thereby tending to direct and carry the heated primary air farther out into the room away from the furnace before the heating air tends to stratify in the room.

The walls and 112 of the secondary air chamber also function as radiant heat reflecting shields between the primary chamber and the exterior walls of the furnace, and of course the same is true of the side, rear and top walls of the primary chamber relative to the combustion chamber.

From the foregoing description, it will now be apparent that furnace 10 as described above fulfills the aforestated objects of the invention and provides an attractive, recessed, sealed combustion heating system which is both economical and versatile.

I claim:

1. A combustion type space heater adapted for upright wall mounting adjacent a space to be heated including in combination (a) heat generating means including a combustion chamber,

(b) a combustion air inlet duct communicating with said combustion chamber,

(c) an outlet flue communicating with said combustion chamber,

(d) a primary air heating chamber at least partially surrounding said combustion chamber,

(e) a cold air inlet duct interconnecting the lower region of the heated space to which said heater is directly exposed with said primary chamber,

(f) a hot air outlet interconecting the upper region of said primary chamber and the heated space adjacent the heater,

(g) a secondary air heating chamber in heat exchange relation with said primary chamber and separated from said combustion chamber by said primary chamber,

(h) an inlet interconnecting the upper region of said secondary chamber with the heated space above said primary chamber outlet and communicating therewith via the heated space, and

(i) a blower having an inlet communicating with said secondary chamber and an outlet adapted to be connected to a hot air distribution duct.

2. The combination set forth in claim 1 wherein said blower is disposed in said cold air inlet duct.

3. The combination set forth in claim 1 wherein said primary air heating chamber comprises an inner casing with vertical rear and side walls and a horizontal top wall spaced from said combustion chamber, wherein said secondary chamber comprises a horizontal top wall, a vertical rear wall and side Wall means connecting said top and rear walls of said inner and outer casings along the side edges thereof so as to define a flow space above said top wall and behind said rear wall of said inner casing, said rear and top walls of said inner casing forming a common Wall between said primary and secondary chambers, and an outer casing defining with said top and rear walls of said secondary chamber at least a portion of said combustion air inlet duct.

4. The combination set forth in claim 3 wherein said blower is disposed in said cold air inlet duct, said outer casing having a bottom wall defining the bottom walls of said cold air inlet and said secondary chamber, said blower inlet being connected through said rear wall of said inner casing to the lower end of said secondary chamber and said blower outlet being connected through said bottom wall of said outer casing.

5. The combination set forth in claim 3 wherein said outer casing has a horizontally extending top wall spaced above said top wall of said secondary chamber and a vertical rear wall connected to the rear edge of said horizontal top wall of said outer casing and spaced horizontally from said vertical rear wall of said secondary chamber, said combustion air inlet duct being formed between said top and rear walls of said outer casing and said secondary chamber.

6. The combination set forth in claim 5 wherein said heat generating means includes a burner box mounted below said combustion chamber and above said blower, wherein said combustion air inlet duct has a bottom wall joined to the lower edge of said vertical rear wall of said secondary chamber and to said side and said rear walls of said outer casing generally at the elevation of said burner box, and said combustion air inlet duct includes a pipe extending through the lower end of said vertical rear wall of said secondary chamber, through said rear wall of said inner casing and through a rear wall of said burner box, said pipe forming with said combustion air inlet duct a sealed path for conducting combustion air from above the furnace to the combustion chamber via the burner box.

7. The combination set forth in claim 3 wherein said primary air heating chamber has an air deflecting baflle disposed therein intermediate said combustion chamber and said top wall of said inner casing and having a front edge disposed at said hot air outlet, said baflle extending from said front edge of said baflle upwardly and rearwardly toward said rear wall of said inner casing and terminating spaced from said rear wall of said inner casing.

8. The combination set forth in claim 1 wherein said heater has a vertical front panel with an imperforate intermediate region and first and second louvered regions with louvers therein respectively defining said hot air outlet and said cold air inlet, said first louvers also covering said inlet to said secondary air heating chamber.

9. A combustion type space heater adapted for upright wall mounting adjacent a space to be heated including in combination (a) heat generating means including a combustion chamber,

(b) a combustion air inlet duct communicating with said combustion chamber,

(0) an outlet flue communicating with said combustion chamber,

(d) a primary air heating chamber at least partially surrounding said combustion chamber,

(e) a cold air inlet duct interconnecting the lower region of the heated space to which said heater is directly exposed with said primary chamber,

(f) a hot air outlet interconnecting the upper region of said primary chamber and the heated space adjacent the heater, and

(g) an air deflecting baflle disposed in said primary chamber above said combustion chamber and below a top wall of said primary chamber, said baflle having a front edge disposed adjacent said hot air outlet at about the vertical midpoint thereof and extending away from said hot air outlet upwardly and rearwardly into the primary chamber and defining therewith a bypass space at the rear of said primary chamber.

10. A heating system comprising a heater as defined in claim 1, a plurality of rooms to be heated disposed remote from said space and a hot air distribution duct connecting said blower outlet with said rooms, said distribution duct communicating said rooms with said secondary chamber via said blower in both the on and off conditions of said blower.

References Cited UNITED STATES PATENTS 2,241,025 5/ 1941 Wedderspoon. 2,281,874 5/ 1942 Funk. 3,082,758 3/ 1963 Heiman. 3,171,402 3/1965 Carlson.

JAMES W. WESTHAVER, Primary Examiner.

US. Cl. X.R. 126-116 

